This invention relates to processes and methods for preparing calcium, normal and overbased sulfurized alkylphenate compositions which are substantially free of the oxidation products of polyol promoters. In a further aspect the invention relates to lubricating compositions and concentrates containing such compositions.
Group II metal overbased sulfurized alkylphenate compositions (sometimes referred to as "overbased phenates") are useful lubricating oil additives which impart detergency and dispersancy properties to the lubricating oil composition as well as providing for an alkalinity reserve in the oil. Alkalinity reserve is necessary in order to neutralize acids generated during engine operation. Without this alkalinity reserve, the acids so generated would result in harmful engine corrosion.
The preparation of overbased phenates is well known in the art and is described, for example, in U.S. Pat. Nos. 2,680,096; 3,178,368; 3,367,867; 3,801,507; and the like. The disclosures of each are incorporated herein by reference in their entirety. Typically, overbased phenates have been prepared by combining under elevated temperatures an alkylphenol, a neutral or overbased hydrocarbyl sulfonate, a high molecular weight alcohol, lubricating oil, a Group II metal oxide, hydroxide or a C.sub.1 to C.sub.6 alkoxide sulfur and a polyol promoter, typically an alkylene glycol, to the heated mixture. The water of reaction is removed and carbon dioxide added. Uncombined CO.sub.2 is removed and the reaction vessel is then further heated under vacuum to remove the alkylene glycol, water and the high molecular weight alcohol. The product is overbased by incorporation therein of hydrated lime and carbon dioxide. Typically an alkylene glycol is used to promote both the neutralization and sulfurization and also to facilitate overbasing.
However, a problem is encountered when the alkylene glycol or other polyol promoter is employed in the presence of significant amounts of sulfur. Specifically, under such reaction conditions, the alkylene glycol or other polyol promoter is oxidized (for example, ethylene glycol is oxidized to the calcium salt of oxalic acid) while the sulfur is reduced to hydrogen sulfide. Such oxidation products are known to be detrimental to engine life. For example, U.S. Pat. No. 4,608,184 discloses that calcium oxalate (an oxidation product of ethylene glycol) adversely effects engine performance as measured by the Caterpillar 1G2 test and suggests a sulfurized phenate synthesis which reduces the amount of calcium oxalate by adding the sulfur to a reaction product mix of a calcium base, alkylphenol and glycol.
U.S. Pat. No. 4,744,921 discloses a method for preparing high TBN Group II metal overbased sulfurized alkylphenate compositions containing less than 10 mole percent unsulfurized alkylphenate which has reduced sediments and exhibits better hydrolytic ability. Sulfurization is conducted using certain sulfurization catalysts without a polyol promoter. The sulfurized phenate is subsequently overbased using an alkylene glycol promoter. The patent does not consider unreacted sulfur or whether the overbasing reaction mixture, using glycol, contains elemental sulfur.
The process suffers from the disadvantage that the preferred organic sulfurization catalysts are very expensive.
U.S. Pat. Nos. 3,437,595 and 3,923,670 disclose processes wherein sulfurization is conducted without a polyol promoter by using either certain basic catalyst in the case of U.S. Pat. No. 3,437,595 as in the case of U.S. Pat. No. 3,923,670 an amount of an alkali metal hydroxide in excess of a catalytic amount. Overbasing follows using glycol and carbon dioxide. Neither patent considers unreacted sulfur and in the case of the process described in U.S. Pat. No. 3,923,670 and the preferred process described in U.S. Pat. No. 3,437,595, the process suffers from the fact that the product contains undesirable alkali metal residues. The use of separation procedures to remove the alkali metal residues from the normal sulfurized phenate is economically undesirable and in some instances the separation procedure introduces problems which interfere with the overbasing process or produce an inferior overbased product.
In the typical preparation of overbased phenates using a polyol, typically ethylene glycol, the polyol is believed to function as a phase transfer agent and/or an activating agent for the alkaline earth metal base in the sulfurization neutralization, and overbasing reactions. It is also known to the prior art that the neutralization can be catalyzed by certain low molecular weight carboxyl acids such as formic and acetic acid or mixtures thereof without the use of a polyol promoter. However, even where a low molecular weight carboxyl acid was used in the sulfurization reaction, a polyol promoter or a lower monohydric alcohol was also used. Thus, regardless of whatever process benefits were obtained by using a carboxylic acid catalyst, deleterious oxidation products were still produced if a polyol promoter was used.
On the other hand if a monohydric lower alcohol promoter were used in place of the polyol promoter, reaction rates necessarily suffered because lower reaction temperatures must be used because of the low boiling point of the alcohol promoter; particularly as the reaction is advantageously conducted at atmospheric pressure or under vacuum to reduce foaming.
U.S. Pat. No. 3,493,516 discloses a process for preparing sulfurized overbased alkaline earth metal alkyl phenates by combining a sulfurized alkyl phenol with lime at elevated temperatures according to known processes and incorporating into the composition a small amount of relatively low molecular weight carboxylic acid or mixtures thereof to form a calcium carboxylate. The patent teaches that the calcium salt of the low molecular weight carboxylic acid may be prepared in situ or prepared prior to introduction into the phenate composition or alternatively, sulfur and alkyl phenol may be added to the reaction mixture in place of the sulfurized alkyl phenol. The patent teaches that the
reaction mixture further contains a high molecular weight alcohol and a polyether alcohol of 2-3 carbon atoms usually ethylene or propylene glycol. Illustrative low molecular weight carboxylic acids described in this patent include formic acid, acetic acid, glycolic acid, glyoxylic acid, propionic acid, maleic acid, etc. Examples 1 and 2 of this Patent describe a sulfurization-neutralization reaction between tetrapropenylphenol, lime and sulfur which is conducted in tridecyl alcohol and glycol in the presence of a mixture of formic acid and glycolic acid.
U.S. Pat. No. Re. 26,811 discloses a process for preparing basic sulfurized phenates and salicylates which comprises reacting at a temperature above 150.degree. C., (A) a phenol or an alkali metal or alkaline earth metal salt thereof, (B) sulfur and (C) an alkaline earth base, in the presence of (D) a carboxylic acid or an alkali metal, alkaline earth metal, zinc or lead salt thereof, and (E) a compound of a formula (ROR').sub.x OH, wherein R is hydrogen or alkyl, R' is alkyl and x is an integer which is at least two if R is hydrogen and at least one if R is alkyl. At column 3, lines 52-55 the patent teaches that the amount of carboxylic acid or salt to be used is generally about 5-20 mole percent preferably about 5-10 mole percent of the amount of phenol in the reaction mixture. Examples of carboxylic acids and salts are set forth by the patent at column 3, lines 38-51 and include formic acid, acetic acid, propionic acid, acrylic acid, capric acid, stearic acid, maleic acid, etc., and salts such as sodium acetate, lithium acetate, potassium stearic, calcium formate, calcium acetate, calcium salt of polyisobutene-substituted succinic acid, zinc acetate, lead propionate and lead caprate. Aliphatic acids containing 2-6 carbon atoms and alkaline earth metals salts thereof, and especially acetic acid and the calcium acetate, are described as preferred. Thus although a carboxylic acid is used, the sulfurization is still conducted in the presence of a polyol promoter; i.e. (ROR').sub.x OH.
U.S. Pat. No. 4,049,560 discloses a process for preparing an overbased magnesium sulfurized phenate which comprises introducing carbon dioxide into a reaction mixture comprising
a. 15-40 wt % of a sulfurized phenol or thiophenol containing one or more hydrocarbyl substituents, or a phenol or thiophenol containing one or more hydrocarbyl substituents, or said phenol or thiophenol containing one or more hydrocarbyl substituents together with sulfur. PA1 b. 5-15 wt % of an organic sulfonic acid, an organic sulphonate or an organic sulphate, PA1 c. 5-15 wt % of a glycol, a C.sub.1 to C.sub.5 monohydric alkanol or C.sub.2 to C.sub.6 alkoxy alkanol, PA1 d. 2-15 wt % of a magnesium hydroxide or active magnesium oxide, PA1 e. at least 0.1 wt % of a C.sub.1 to C.sub.18 carboxylic acid, an anhydride thereof, or an ammonium, an amine salt, a Group I metal or a Group II metal salt of said C.sub.1 to C.sub.18 carboxylic acid, and PA1 f. at least 10% by weight of a diluent oil (including any present in components (a) and (b)).
The carboxylic acid is described as a promoter and is preferably used in an amount of 0.5 to 2.0% by weight and preferably is formic acid, acetic acid, propionic acid, or a butyric acid. But, the reaction mixture also contains a polyol promoter, i.e., a glycol or alkoxyalkanol, or contains a lower monohydric alkanol.
U.S. Pat. No. 5,035,816 discloses a process for preparing sulfurized overbased alkyl salicylates which comprises neutralizing an alkyl phenol with an alkaline earth base in the presence of at least one acid selected from C.sub.1 to C.sub.18 aliphatic carboxylic acid, benzoic acid, benzoic anhydride or mineral acids in the presence of an azeotropic solvent followed by a carboxylation of the neutralized reaction product and sulfurization with sulfur in ethylene glycol. With respect to the neutralization step the patent teaches that C.sub.1 to C.sub.3 aliphatic carboxylic acids, and especially their mixtures, for example the formic acid-acetic acid mixture according to an acetic/formic acid ratio which can range from 0.01/1 to 5/1, preferably from 0.25/1 to 2/1, and especially on the order of 1/1 are preferred. (See column 2, lines 53-58)
European Patent Application 271262 published Jun. 15, 1988 discloses a process for preparing sulfurized based hydrocarbyl phenates which comprises reacting either a hydrocarbyl phenol or a hydrocarbyl phenol and sulfur with an alkaline earth metal base and at least one carboxylic acid having at least carbon atoms in or with (c) either a polyhydric alcohol or an alkyl glycol, alkyl glycol ether, or polyalkylene glycol alkyl ether. The patent further teaches that when using a glycol or glycol ether, it is preferred to use in combination therewith an inorganic halide, for example ammonium chloride, and a lower, i.e., C.sub.1 to C.sub.4, carboxylic acid, for example acetic acid.
European Patent Application 0273588 published Jul. 6, 1988 discloses a process for increasing the TBN of an alkaline earth alkyl phenate which comprises reacting at elevated temperature a sulfurized alkaline earth metal hydrocarbyl phenate, an alkaline earth metal base, a carboxylic acid having at least carbon atoms and either a polyhydric alcohol having 2 to 4 carbon atoms, (di- or tri-) (C.sub.2 to C.sub.4) glycol, alkyl glycol, alkyl glycol ether or a polyalkylene glycol alkyl ether.